The objective of the proposed project is to develop a real time high frequency ultrasound imaging system capable of pulsed Doppler with a frame rate higher than 150 Hz for cardiac applications in small animals. Ultrasound imaging is a well established technology for cardiac imaging on humans. For cardiac imaging in small animals whose hearts beat at a rate higher than 200 beats/minute, the spatial and temporal resolutions of current clinical ultrasonic scanners are far from ideal and simply inadequate for such applications. Furthermore current commercial high frequency ultrasonic scanners developed for small animal imaging and eye imaging in humans are incapable of producing images at a frame rate higher than 30 Hz. The device to be designed and fabricated will be a mechanical sector scanner with a single element transducer capable of imaging the heart of small animals at a frequency from 30 to 50 MHz at a frame rate of at least 150 Hz. The proposed scanner will consist of a probe and an imaging unit that will be based on existing technology and commercial components. The design and fabrication of the probe will be the heart of the project. It will be developed in collaboration with Capistrano Lab by integrating a single element high frequency transducer with an f-number of 2 to 4 with a servo motor system. The USC group has expertise in transducer engineering and imaging system development whereas Capistrano labs Inc. has produced a similar probe which is commercially available but at a lower frame rate. The probe will be designed and built at Capistrano. The imaging unit, the Pulsed Doppler unit, and transducers will be designed and built at USC. System integration of the probe and the imaging console will also be carried out at USC. Upon the completion of this research it is expected that a prototype system will be designed and tested on wire and flow phantoms, excised mouse hearts in vitro and live animals in vivo.